1. Field of the Invention
The present invention concerns in a general manner a device for measuring the ocular parameters of a subject especially the pupillary deviation, and concerns more particularly, a device in which this measurement is made by determining for each eye the position of the reflection on the cornea of a luminous source focused at infinity.
In a more precise manner, the present invention concerns a luminous source for such a device, which source is intended to produce a reflection on the cornea of each eye.
2. Description of the Prior Art
In known devices, such as that described in French Patent published under No. 1.506.352, the luminous source that is used is constituted by a filament lamp. This source which is placed at the focus of a lens constitutes first a fixation point, projected to infinity by the lens, for the subject whose ocular parameters it is desired to measure. The second essential function of this luminous source is to form on the cornea of each of the subject's eyes a reflection that can be observed by the operator of the device.
The operator who observes the subject's eyes and consequently observes each corneal reflection can superimpose on each of them a horizontally movable vertical reticle so as to determine the pupillary distance between the centers of the subjects pupils and a vertically movable horizontal reticle to determine the distance separating the centre of each pupil from the lower part of a spectacle frame worn by the subject.
The luminous source must have a range sufficient to be able to produce on the cornea of each eye a reflection, observable by the operator but it must also be small enough to completely fix at infinity the subject's stare. These two antinomic conditions lead to using a luminous source having a size such that it impairs the measuring precision of the device, taking into account especially the difficulty for the operator of centering a reticle on a reflection of a dimension clearly greater than the width or the thickness of the reticle .
The present invention overcomes this major drawback by proposing a luminous source for fulfilling the two conditions set out above.
The luminous source according to the invention is essentially characterized in that it comprises a first extended substantially perimetric emitting zone, adapted to produce on the cornea of each eye of the subject a reflection that can be observed by the operator and a second point emitting zone disposed at the centre of the first zone and constituting the fixation point of the subject's stare.
Accordingly, the subject can fix his sight on the second point emitting zone, this second zone being small enough not to produce any corneal reflection observable by the operator.
The first perimetric extended emitting zone will produce for itself a corneal reflection with perfectly defined outlines, and a dark central part, allowing the operator an easy and rapid centering of the reticles on the said corneal reflection.
According to a first embodiment of the invention the wavelengths of the first and second emitting zones are different and preferably have a value respectively comprised between 6.500 and 8.000 angstroms and between 5.000 and 6.000 angstroms.
According to another preferred embodiment, the first perimetric emitting zone, is constituted by four electroluminescent diode strips, each of them being centered on one side of a square.
In an equally advantageous manner, the second emitting zone is constituted by a point electroluminescent diode.